Generally, with a conventional finder device of a camera, and in particular, with a lighting format finder device such as is shown in FIG. 5, the light of a finder image which has passed through multiple lens elements of an objective lens 7 enters a roof prism 8. After the direction of travel has been changed by means of the roof prism 8, the light enters into a prism 9. After being reflected multiple times within the prism 9, the light passes through an eyepiece lens system 10 (shown herein as a single lens) and then exits the finder device. Between the roof prism 8 and the prism 9 is positioned a frame body 53 which is integrally attached to a finder frame main body 11. Frame body 53 includes two spaced-apart pins 14 which protrude from the frame body 53 on the side of the objective lens 7. On the two spaced-apart pins 14 are mounted a screen format switchable mask 16 which is held in place by a mask pressure plate 1.
The screen format switchable mask 16 is for switching the format of the image aperture, and is normally capable of switching to a standard format (C), a high format (H), and a panorama format (P). Such a screen format switchable mask is disclosed, for example, in Japanese Laid Open Patent Application H6-82882.
The light which passes through the roof prism 8 progresses by means of the screen format switchable mask 16 without any hindrance and is then transmitted to the prism 9. As illustrated in FIG. 6, on the surface of the light output side of the roof prism 8 is formed an auto focus target mark (AF) and a close range correction mark 44. The close range correction mark 44 is established such that it falls within the field of vision of the photographer when the object to be photographed is viewed through the eyepiece lens system 10 (FIG. 5).
In a conventional finder device constructed in the manner described above, the auto focus target mark AF and the close range correction mark 44 are formed on the surface of the light output side of the roof prism 8, and the operation of forming the auto focus target mark AF and the close range correction mark 44 on the roof prism 8 is such that the roof prism 8 itself may easily be broken during the process. As a result, there is a problem in that the defect rate is too high.